Flares are regularly used to combust hydrocarbons and hazardous air pollutants in refineries, chemical plants and other oil and gas related operations. Certain of these facilities are required to meet minimum BTU Net Heating Values (NHVs) for gas streams fed to flares in order to assure combustion of hydrocarbons and hazardous air pollutants (HAPs). NHV requirements may apply to the gas in the feed line or at the flare tip depending on applicable rules for the specific facility type.
As an example, new rules applicable as part of the EPA's revised Refinery Sector Rule (RSR) eliminate previous compliance exemptions for process start up, shut down and malfunction (“SSM”) events which can all result in substantially increased gas flow to flares. Under the revised new rules, emergency flaring, flow from pressure relief device (PRD) venting, sulfur recovery plants catalytic cracking units and other processes must now meet new NHV requirements.
Most, but not all, PRD release and malfunction events will release hydrocarbon rich streams which are high in BTU NHV and inherently compliant with the rule. Conversely, nitrogen is regularly used to purge hydrocarbons and hazardous air pollutants from process equipment, feed lines, storage tanks and other areas in oil and gas facilities. These nitrogen purge streams can be very high flow and largely composed of Nitrogen which has a NHV of Zero (0) BTUs. Nitrogen dilution of gas streams will cause them to fall below regulatory NHVs and cause a facility to be out of compliance with regulatory standards.
Facilities will regularly need to feed higher BTU supplemental fuel gas to flare streams to increase the stream NHV in order to stay in compliance. Similar situations exist for chemical plants and other operations who must meet requirements outlined in other rules.
There are several source options for various supplemental fuel gases within plant operations including natural gas supplied by pipeline, process generated products such as hydrogen, propane, propylene or butane and light ends fuel gas produced from distillation and other processes. And, some facilities have already made needed connections to their flare streams to meet requirements for most or all cases.
Other facilities, though, are faced with technical and logistics challenges related to these requirements including the following:                The expense of running connections within the facilities from fuel gas sources to flare feed lines. One example noted that the flares are on one corner of the site and the source gas is on the opposite corner with a resultant project cost that is too high to consider.        Restricted and/or insufficient flow from natural gas utilities. Restricted flow could be a result of other critical users on a line that would be adversely affected by a plant pulling very high volumes of gas        An inadequate supply of surplus fuel gas from process sources may also prove to be a problem. For example a product that might otherwise be available is required to feed new or bottle-necked plant processes.        Pipeline supplied natural gas exists and is possibly already connected, but the available volume is inadequate to meet highest flow, and        Inavailability of normal supplemental fuel gas supply due to partial or overall plant outage.        